Oil is a nonrenewable natural resource having great importance to the industrialized world. Over the last century, the consumption of oil has increased dramatically and has become a strategic commodity, leading to the development of alternative sources of crude oil such as oil sands and oil shales. As used herein, oil sands are a granular or particulate material, such as an interlocked skeleton of sand, with pore spaces occupied by bitumen (an amorphous solid hydrocarbon material totally soluble in carbon disulfide), and oil shale is a rock containing kerogen (a carbonaceous material that which gives rise to crude oil on distillation). The vast majority of the world's oil sands deposits are found in Canada and Venezuela. Collectively, oil sands deposits contain an estimated 10 trillion barrels of in-place oil. Oil shales are found worldwide with large deposits in the U.S. Collectively, oil shale deposits contain an estimated 30 trillion barrels or more of in-place oil. It is to be understood that a reference to oil sands is intended to include oil shales and vice versa.
Bitumen is typically an asphalt-like substance having an API gravity commonly ranging from about 5° to about 10° and is contained within the pore space of the oil sands. Bitumen cannot be recovered by traditional oil well technology because it will not flow at ambient reservoir temperatures. To overcome this limitation, near surface oil sand deposits are excavated by surface mining methods, while bitumen in deeper deposits is recovered by in situ techniques, which rely on steam or diluents to mobilize the bitumen so that it can be pumped out by conventional oil recovery methods. The bitumen is recovered from the surface excavated oil sands by known separation methods, and the bitumen, whether derived from surface mining or in situ processes, sent to upgrading facilities where it is converted into crude oil and other petroleum products. Underground mining techniques have been largely unsuccessful in mining deeper oil sands due to high mining costs and unstable overburden conditions.
Existing methods for recovering oil from oil sands have numerous drawbacks. Surface mining techniques are typically only economical for shallow oil sands deposits. It is common for oil sands deposits to dip and a significant part of the ore body may be located at depths that are too deep to recover by surface mining methods. As a result, most of the oil sands deposits are unprofitable to mine. Surface mining requires large areas to be stripped of overburden which then must be moved to other areas for storage. The tailings from the bitumen separation process typically require large tailings ponds complexes in which the tailings are treated before the mined land can be reclaimed. The costs of stripping overburden, building and maintaining tailings ponds and eventual land reclamation costs can be high, particularly for deeper oil sands deposits. Because of the large scale of these operations, the short and long term environmental impact and associated costs of surface mining can be substantial. In situ techniques are disadvantaged in that a relatively large amount of energy is consumed per unit energy recovered in the bitumen.
A significant portion of oil sands deposits lie too deep for economical recovery by surface mining and are too shallow for effective in-situ recovery. Other oil sands deposits, though located at shallow depths, are located under surface features that preclude the use of surface mining. For example, oil sands deposits can be located under lakes, swamps, protected animal habitats and surface mine facilities such as tailings ponds. Estimates for economical grade bitumen in these in-between and inaccessible areas range from 30 to 100 billion barrels.